Spark plug seal



April 19, 1966 H. G. SCHURECHT ETAL 3,247,132

SPARK PLUG SEAL Filed April 5, 1963 llllll 55" 6070 GLASS Al looq LOO70 Bi, Pb OR. PkwSn Z INVENTOR.

- 5-- HAREY C5. SLHUEECHT' @MK f g o ATTOQ NE V5 United States Patent 3,247,132. SkARK PLUG SEAL Harry G. Schurecht, Si. Petershurg, Fla., and Robert H. Insley, Royal Oak, Micli., assignors to The (Ihampion Spark Plug Company, Toledo, Ohio, a corporation of Delaware Filed Apr. 5, 1963, Ser. No. 270,897 7 Claims. or. 252-514 This invention relates broadly to spark plugs and, more particularly, to a substantially gas impervious, electrically conducting sealing material for use in spark plugs and the like.

Numerous and varied suggestions have heretofore been made in regard to compositions for use in effecting a seal between a ceramic and a metallic part of a spark plug. For example, it has been proposed to render such sealing compositions electrically conducting in order to eliminate the need for a wire electrode extending completely through the bore of the insulator, and also to enable the use of two axially separated metal or metal alloy electrodes, each possessing certain chemical and physical properties so that it is better adapted to withstand the particular conditions peculiar to the environment existing in service at the firing end or at the 'terminal end of the spark plug, as the case may be. Adrnixtures of various powdered conducting metals, such as copper, nickel, tungsten and molybdenum, with a glassy sealing material, have been proposed for this purpose, the powdered metals being employed in an attempt to provide a satisfactory conducting path through the glass sealing material to carry the high tension current from one of the electrode parts to the other. However, so far as is known, none of the seals produced from such admixtures has been found to be completely satisfactory.

Three problems have been found to exist in attempting to produce a satisfactory electrically conducting glass seal for use in spark plugs. The first such problem is the develpment of a composition which exihibits a very low resistance to the passage of electric current and at the same time additionally furnishes a structure, upon firing, which forms an excellent gas impervious seal between the metal and ceramic parts of the spark plug assembly which, of course, possess different coefficients of thermal expansion. The second such problem is the development of a composition which retains both excellent sealing and electrical conductivity properties under operating conditions during the expected service life of the assemby produced therefrom. In this respect, it has been found that although many compositions seemingly appear to be well suited for spark plug use, having an extremely low resistance when first tested, such compositions greatly increase in resistance during the normal service life thereof, becoming finally, in effect, substantially an insulator or semiconductor rather than a satisfactory conductor. Although the reason for the surprising change in electnical properties is not completely understood, the effect of such change is to render the compositions completely unsuitable for spark plug use. The third problem exists in the development of an electrically conductive seal material which will fuse at a temperature below the recrystallization temperature of the center electrode.

It has now been discovered, and the instant invention is based on such discovery, that an excellent electrically conducting, substantially gas impervious sealing material can be produced from an admixture of a lead-silicate glass, aluminum metal, and one or more electrically conducting materials of a particular group of metals and metalloids, namely, copper, silicon, lead, bismuth, leadtin solders, nickel, platinum, chromium and cobalt.

3,247,132 Patented Apr. 19, 1966 It is, therefore, an object of the invention to provide an improved spark plug assembly.

It is another object of the invention to provide a sealing material for use in spark plugs which wholly or substantially eliminates the leakage of gas therethrough from an engine cylinder.

It is a further object of the invention to provide a substantially gas-impervious sealing material which possesses an extremely low resistance to the passage of high tension, electric current therethrough.

It is a still further object of the invention to provide an electrically conducting, substantially gas impervious sealing material for use in spark plugs, which material does not substantially increase in electrical resistance during the normal service life of spark plugs employing such material.

Other objects and advantages will in part be apparent and will in part appear hereinafter. For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description and accompanying drawing in which:

FIG. 1 is a central, vertical sectional view of a spark plug insulator and electrode assembly including an electrically conducting seal produced in accordance with, and embodying, the present invention; and

FIG. 2 is a triangular coordinate composition diagram the shaded area of which shows the general range of proportions in which the metal and metalloid components thereof can be blended for the production of sealing materials according to the present invention.

Referring now to FIG. 1, reference numeral 10 indicates a ceramic insulator having a longitudinal bore 11 extending centrally therethrough. The bore is provided with an internal shoulder 12 adjacent the lower end of the insulator to provide a seat for a lower, sparking electrode part 13.

An upper or terminal electrode part 14 is preferably made of cold rolled steel or other good heat conducting and electrically conductive material, and is provided with a shoulder 15 to limit the extent of insertion of the part into the bore.

An electrically conducting, substantially gas impervious, sealing material produced in accordance with the invention, and indicated at 16, is disposed generally between the electrode parts 13 and 14 and in sealing relation therewith as well as with the bore of the insulator. The lower end of the electrode part 14 is preferably provided with a roughened surface such as projections 17 or the like, in order to better anchor the electrode in the sealing material.

In producing the spark plug assembly, illustrated in FIG. 1, the lower electrode part 13 may first be inserted into the insulator bore 11 and seated on the shoulder 12 provided therein. A predetermined quantity of a sealing admixture having a composition in accordance with the invention, either in powder form or in the shape of a pressed, cylindrical pellet, is next inserted into the bore. The upper electrode part 14 is then advanced to the position shown in FIG. 1. Thereafter, the assembly is heated in a suitable furnace to a temperature sufficient to fuse the sealing admixture and cause a desired reaction to take place between the various components thereof, as will be subsequently explained in more detail.

The novel, electrically conducting sealing material 16 can be within either of two main groups, with respect to the percentage by weight of lead-silicate glass found in the seal.

A low glass group includes those seals which contain 55 parts by weight to 60 parts by weight of a lead-silicate glass, while a high glass group includes those seals which contain 60 parts by weight to 85 parts by weight of a lead-silicate glass.

An electrically conducting sealing material is produced by firing to a temperature from about 1250 F. to about 1750 F. a composition consisting essentially of one selected from the group consisting of compositions of from 55 parts to 60 parts of a lead-silicate glass, from 6 parts to '20 parts of aluminum metal, and from 15 parts to 40 parts of at least one electrically conducting material selected from the group consisting of nickel, platinum, chromium, cobalt, bismuth, silicon, lead, silver, copper, and lead-tin solders having a melting point not higher tha 350 C., and compositions of from 60 parts to 85 parts of a lead-silicate glass, from 10 parts to 20 parts of aluminum metal, and from 10 parts to 40 parts of at least one electrically conducting material selected from the group consisting of nickel, platinum, chromium, cobalt, bismuth, silicon, lead, silver, copper, and lead-tin solders having a melting point not higher than 350 C.

An excellent sealing material according to the invention, and within the low glass group, is produced by firing to a temperature from about 1250 F. to about 1750 F., a composition consisting essentially of from 55 parts to 60 parts of a lead silicate glass, from 8 parts to 20 parts of aluminum, from 2 parts to 28 parts of at least one high melting element selected from the group consisting of silicon, nickel, copper, silver, platinum, chromium, and cobalt, and from 7 parts to 29 parts of at least one electrically conducting material selected from the group consisting of bismuth, lead, and lead solders having a melting point not higher than 350 C. Preferably, the sealing composition according to the invention, within the low glass group, consists essentially of from 55 parts to 60 parts of a lead-silicate glass, from 8 parts to 15 parts of aluminum, from to 0.5 part of graphite, from 0 t0 2 parts by weight of bentonite, from 2 parts to 28 parts of at least one high melting element selected from the group consisting of silicon, nickel, copper, silver, platinum, chromium, and cobalt and from 7 parts to 29 parts of at least one low melting metal selected from the group consisting of bismuth, lead, and lead solders havinga melting point not higher than 350 C. The optimum proportions of the aluminum, bismuth, lead, lead solder, silicon, nickel, copper, silver, platinum, chromium and cobalt, based upon the total thereof, are represented by the shaded portion of FIG. 2 of the drawmg.

A preferred composition, within the low glass group, which has been found to possess particularly excellent properties is one consisting of from 57 parts to 58 parts of a lead-silicate glass, from parts to 14.5 parts of aluminum, from 2 parts to 27 parts of at least one high melting element selected from the group consisting of silicon, nickel, copper, silver, platinum, chromium, and cobalt, and from 7 parts to 27 parts of at least one low melting metal selected from the group consisting of hismuth, lead, and lead solders having a melting point not higher than 350 C., and wherein the proportions of the aluminum, bismuth, lead, lead solder, silicon, nickel, copper, silver, platinum, chromium and cobalt, based upon the total thereof, are represented by the shaded portion of FIG. 2 of the drawing.

An excellent sealing material according to the invention, and within the high glass group, is produced by firing to a temperature from about 1250 F. to about 1750 F., a composition consisting essentially of from 60 parts to 72 parts of a lead-silicate glass, from 10 parts to parts of aluminum, and from 10 parts to 30 parts of at least one electrically conducting material selected from the group consisting of nickel, platinum, chromium, cobalt, bismuth, silicon, lead, silver, copper, and lead-tin The terms percent and parts, as used herein, and in the appended cla1 ms refer to percent and parts by Weight, unless otherwise indicated.

solders having a melting point not higher than 350 C. Preferably, the sealing composition according to the invention, within the high glass group, consists essentially of from 63 parts to 68 parts of a lead-silicate glass, from 10 parts to 13 parts of aluminum, from 0 to 0.5 part of of graphite, from 0 to 2 parts of bentonite, and from 17 parts to 28 parts of at least one electrically conducting material selected from the group consisting of nickel, platinum, chromium, cobalt, bismuth, silicon, lead, silver, copper, and lead-tin solders having a melting point not higher than 350 C.

A preferred composition, within the high glass group, which has been found to possess particularly excellent properties is one consisting of from 65 parts to 67 parts of a lead-silicate glass, from 10 parts to 13 parts of aluminum, from 0 to 0.5 part of graphite, from 0 to 2 parts of bentonite, from 2 parts to 5 parts of silicon, and from 15 parts to 20 parts of a lead-tin solder having a melting point not higher than 350 C.

It has been found to be essential that the glass employed in the sealing admixture according to the invention be of the lead-silicate type, i.e., include lead oxide and silica in its formulation. In this respect, various other known glass-forming ingredients, for example A1 0 alkali metal oxides, B 0 ZnO, etc. may be present in the glass formulation in addition to lead oxide and silica, and the term lead-silicate glass as used herein and in the appended claims is defined as including such additional glass forming ingredients, it only being essential that the glass include at least lead oxide and silica in its formulation. For example, particularly excellent results have been obtained when employing lead borosilicate glass in the admixture according to the invention.

In addition to the use of a lead-silicate glass being es sential, it has also been found essential to include one or more metals or metalloids, namely, bismuth, silicon, copper, lead, silver, nickel, platinum, chromium, lead-tin solder or cobalt in the admixture, the total of such elements being not less than 10 parts nor more than 40 parts of the admixture. Tests have shown that the presence of at least one of these electrically conducting materials is essential in order to obtain the excellent electrical properties characteristic of seals produced in accordance with the present invention. In this respect, it has been determined that the existence of one of the extremely important properties of seals produced in accordance with the invention, namely, that they do not materially increase in electrical resistance during service, is essentially due to the presence of one or more of the above electrically conducting materials. In addition, it has been found that the presence of such materials enables a Wider maturing temperature range to be employed in firing the seal admixture which is of great importance in obviating the necessity for precise furnace or temperature control when producing the seals in accordance with the invention.

It has also been determined to be essential to include aluminum metal in the admixture in the range hereinbefore set forth. It is believed, although the invention is not limited to the following theoretical explanation, that a pyrothermic reaction, known to occur during firing to produce the sealing materials of the invention, causes a desirable chemical reaction to take place between the aluminum metal and the glass. It has been found that this pyrothermic or thermite type reaction causes the seal to become an excellent electrical conductor. In this respect, X-ray examinations of glass seal compositions fired in accordance with the present invention indicate that the conducting portion of the glass seal consists essentially of the metals or metalloids which were added to and remain in the seal material after firing along with metallic lead which has been prodced throughout the seal as a result of the reduction of the lead-silicate glass by the aluminum metal.

The unexpected results obtained in accordance with the invention are still more pronounced by the fact that similar results are not obtained by merely adding selective amounts of lead and silicon metal powder to glass seal compositions containing the aluminum metal. Tests on such fused compositions have shown them not to be electrically conducting. It is evident, therefore, that a unique cooperation takes place between the components of the composition embodying the present invention, when fired and matured in the previously designated temperature range, resulting in a sealing material having excellent electrical conductivity and sealing properties. In the above respect, it has been determined that seals having an electrical resistance of less than 5 ohms are extremely well suited for use in substantially all present day spark plug applications. In addition to the low electrical resistance required of seals in order for them to perform satisfactorily, it is necessary that such seals can withstand high gas pressures without leakage. It has been determined that seals capable of withstanding pressures of 1000 p.s.i. or higher without leaking perform satisfactorily under essentially all operating conditions to Which they are normally subjected.

The pyrothermic reaction that takes place upon firing the sealing admixture in accordance with the invention is important in other respects in addition to those above mentioned. For example, the occurrence of the reaction enables satisfactory firing at a lower furnace temperature than would normally be suitable. Further, the high temperature required to effectively fuse and mature the seal admixture, since it results in part from the pyrothermic reaction, is substantially localized to the area of the seal itself. This is important in that it is extremely desirable to employ an upper or terminal electrode part made from cold rolled steel, which would be deformed at the high furnace temperatures presently necessary to effectively mature and fuse sealing admixtures. Also because of the localized heating effect, the problem of recrystallization and consequent intergranular corrosion and ultimate failure of the nickel or nickel alloy forming the lower sparking electrode part is substantially eliminated. In addition the localized heating effect allows the lower end of the electrode 13 to remain cooler so that its end does not become rounded.

In order to determine the range of temperatures to which sealing admixtures produced in accordance with the invention can be fired to obtain the excellent high elec-.

trical conductivity and sealing properties necessary to insure proper performance thereof in spark plug assemblies under operating conditions, numbers of admixtures were fired at various temperatures and tests were made thereupon for measuring gas leakage and electrical conductivity. It has been found that seal compositions according to the invention possessing a wide maturing temperature range are usually the most dependable,

since less care need be taken in respect to furnace control during firing. However, if furnaces having accurate controls and therefore small temperature variations are employed, admixtures according to the invention with relatively narrow maturing ranges may be successfully utilized. It has been found that generally maturing or firing temperatures within the range of 1250 to about 1750 F. are satisfactory, with the majority of seal compositions produced in accordance with the invention maturing between about 1300" F. and 1650 F.

One type of seal composition that has been found to be particularly reliable and possess a wide maturing temperature range is that containing silicon and lead-tin solder in addition to, of course, aluminum metal and lead silicate glass. Excellent results have been obtained with these silicon-lead-tin solder type seals produced from a As determined by electrical resistance measurements on .3 gram portions of the Various seal compositions, pressed,

with a force of approximately 400 'to 600 pounds, into cylinbatch admixture having a composition of 55 parts to 60 parts of a lead-silicate glass, 3 parts to 10 parts of silicon, 20 parts to 30 parts of lead-tin solder, 8 parts to 12 parts of aluminum, 0 to 0.5 part of graphite and 0 to 2.0 parts of bentonite, said batch being fired at a temperature within the range of about 1300 F. to about 1650 F. A preferred composition which has been found to possess particularly excellent properties is that consisting of 57 to 58 parts of a lead borosilicate glass, 4 parts to 8 parts of silicon, 23 parts to 27 parts of lead-tin solder, 8 parts to 10 parts of aluminum, 0.5 part of graphite, and 2.0 parts of bentonite.

Another type of seal composition that has been found to be particularly reliable and possess a wide maturing temperature range is that containing silicon and bismuth in addition to, of course, aluminum metal and leadsilicate glass. Excellent results have been obtained with these silicon-bismuth type seals produced from a batch admixture having a composition of 55 parts to 75 parts of a lead-silicate 'glass, 3 parts to 7 parts of silicon, 10 parts to 30 parts of bismuth, 10 parts to 14 parts of aluminum, 0 to 0.5 part of graphite and 0 to 2.0 parts of bentonite, said batch being fired at a temperature within the range of about 1300 F. to about 1650 F. A preferred composition which has been found to possess particularly excellent properties is that composed of 60 parts of a lead borosilicate glass, 4 parts of silicon, 24 parts of bismuth, 12 parts of aluminum, 05 part of graphite, and 2.0 parts of bentonite.

As is readily apparent from Table I (following) all the seals produced from admixtures containing silicon and lead-tin solder or silicon and bismuth, in addition to a lead silicate glass and aluminum metal in the ranges previously set forth, adequately meet the stringent requirements necessary of seals to assure proper performance thereof under operating conditions. Further, it

has been found that these seals, having the extremely low initial electric resistances recited, do not materially increase in resistance during the normal operating life of spark plug assemblies produced therefrom.

Various other seals produced from admixtures containing various combinations of the elements previously enumerated, in addition to lead-silicate glass and aluminum, within the general range set forth, have been successfully employed in spark plug assemblies. For example particularly excellent results have been obtained when producing seals from batch admixtures containing, in addition to aluminum and lead-silicate glass, namely, silver; silicon, bismuth and lead; silicon and lead; silicon and copper; and bismuth.

In this respect further, Table I illustrates several specific vitreous sealing compositions embodying the present invention. Samples were prepared by dry milling powders of the various components until a homogeneous mixture was achieved. Several 0.3 gram samples of the various compositions were then pressed, with a total force of 500 pounds, into a cylinder 0.320" in length, and having a diameter of 0.149". Some of the resulting cylinders were then employed in producing spark plug assemblies, such as that shown in the drawing, and the assemblies then fired to the various temperatures set forth in Table I. After the assemblies were removed from the furnace and cooled, they were subjected to a gas leakage test. This test consisted of screwing the spark plugs in a female-type socket, such socket being connected to a high pressure gas source through a suitable reducing valve. The firing procedure consisted in placing the cylinder or spark plug assembly in a furnace previously heated to the designated temperature; the furnace was allowed to come back to temperature; and the assembly was held at such temperature for twenty minutes. It should be noted that the examples listed in Table I are given for purposes of illustration only and are in no way intended to be limitative of the present invention.

factorily under operating conditions, have a relatively TABLE I Firing temperature F.)

Glggs Seal Composition (parts by weight) A Glass A 1 57.5 1st Sample:

50/50=Pb/Sn solder- 24. Leakage test (p.s.1.) 1, 000+ 1, 000+ 1, 000+ 1, 000+ 1, 000+ Silicon 8. 0 Electrical resistance (ohms) 0. 65 0.40 .41 0.45 0.25 Aluminum. 8.0 2nd Sample: Graphite... 0.5 Leakage test (p.s.1.) 1, 000+ 1, 000+ 1, 000+ 1, 000+ 1, 000+ Bentonite 2.0 Electrical resistance (ohms) 0. 55 0.70 .54 0.45 0.24

B- Glass A 57. 1st Sample:

50/50=Pb/Sn solder 28. 0 Leakage test (p.s.1.) 1, 000+ 1, 000+ 1, 000+ 1, 000+ 1, 000+ Aluminum 6. 0 Electrical resistance (ohms) 0.0 5. 0 4. 0 3.0 3. 2 Silicon- 6. 0 2nd Sample: Graphite 0.5 Leakage est (p.s.1.) 1, 000+ 1, 000+ 1, 000+ 1, 000+ 1, 000+ Bentornte 2.0 Electrical resistance (ohms) 9. 7 4. 0 .4 2. 2 3. 0

C. Glass A. 59. 4 1st Sample: 7

Silicon 4. 0 Leakage test (p.s.i.) 1, 000+ 1, 000+ 1, 000+ 1, 000+ 1, 000+ Bismuth. 2317 Electrical resistance (ohms) 8. 13 1. 03 0.15 0.15 0. l0 Graphite. 0.5 2nd Sample: AlullllllullL 11.9 Leakage test (p.si.) 1, 000+ 1, 000+ 1, 000+ 1, 000+ 1, 000+ Bentonite 0. 5 Electrical resistance (ohms) .53 0. 40 0.34 0.15 0.13

65. 2 1st Sample: 19. 6 Leakage test (p.s.1.) 1, 000+ 1, 000+ 1, 060+ 1, 000+ 1, 000+ 6.5 Electrical resistance (ohms) l. 1 9. 3 4. 3 4. 2 7. 4 6. 5 2nd Sample: 0. 2 Leakage test (p.s.1.) 1, 000+ 1, 000+ 1, 000+ 1, 000+ 1, 000+ 2. 0 Electrical resistance (ohms) 1. 0 8.3 3. 2 4.0 4.4

64. 5 1st Sample:

2.1 Leakage test (13.5.1.) 1', 000+ 1, 000+ 1, 000+ 1, 000+ 100- 12, 9 Electrical reslstance (ohms) 0.90 .40 0. 1.00 0.80

6. 9 2nd Sample: 11.2 Leakage test (p.s.1.) 1, 000+ 1 000+ 1, 000+ 1, 000+ 1, 000+ 0.5 Electrical resistance (ohms) 0.96 0.40 0.20 .40 0. Bentonite 1. 9

E Glass A 64. 3 1st Sample: 3. 2 Leakage test (p.s.i.) 1, 000+ 1, 000+ 1, 000+ 1, 000+ 100- 19. 2 Electrical resistance (ohms). 5. 87 .47 .37 0, 24 1. 24 10. 9 2nd Sample:

0.5 Leakage test (p.s.1.)- 1, 000+ 1, 000+ 1, 000+ 1 000+ 2 500 1. 9 Electrical resistance (ohms) .67 0. 37 37 .27 0.75

' G Glass A 68.3 1st Sample:

Silver 19. 5 Leakage test p.s.i.) 100- 1, 000+ 1, 000+ 1, 000+ 1, 000+ Aluminum. 9. 8 Electrical resistance (ohms) 1. l 70 0. 52 0. 38 0. 24 Graphite-.. 00.5 2nd Sample: Bentonite 1.9 Leakage test (p.s.1.) 100- 1,000+ 1, 000+ 1 000+ 1,000+

Electrical resistance (ohms) 1. 0 00 0. 52 4O 0. 78 100. 0

H Glass A 68.3 1st Sample:

Silicon. 5. 9 Leakage test (p.s.1.) 1, 000+ 1, 000+ 1, 000+ 1, 000+ 1, 000+ Lead powd 11.7 Electrical resistance (ohms) 0, 62 0, 31 0, 28 0 25 0, 24 Aluminum 11.7 2nd Sample: Graphite.-- 0. 5 Leakage test (p.s.i.) 1,000+ 1, 000+ 1 000+ 1, 000+ 1, 000+ Bentonite 1.9 Electrical resistance (ohms) o. 24 0. 28 25 0.28

I Glass A 71. 1 1st Sample:

Silicon 6. 5 Leakage test (p.s.1.) 1, 000+ 1, 000+ 1, 000+ 1, 000+ Bismuth 9. 7 Electrical resistance (ohms) 1. 2 1. 2 4. 5 0.70 Aluminum 10. 3 2nd Sample; Gra hite 0.5 Leakage test (p.s.i.) 1, 000+ 1, 000+ 1, 000+ 100- Bentonite 1. 9 Electrical resistance (ohms) 1. 3 0. 6 0. 5 1. 00

; ldGliss A consists essentially of: S10 40.9 percent; PbO 35.2 percent; A1 0 5.2 percent; N320 1.4 percent; K20 1.3 percent; and B303 14.0 percent.

Seals produced from admixtures in Which silver is the sole addition element, although adequately meeting the requirements previously set forth and performing satisnarrow maturing range in comparison to some of the other specific admixture combinations above recited, namely, from approximately 1475 F. to approximately 1650 F. The best results have been obtained with this 70 type seal when employing an admixture comprising from parts to 75 parts of a lead-silicate glass, from 15 parts to 25 parts of silver and from 10 parts to 12 parts of aluminum, small amounts of graphite and bentonite in the ranges previously set forth being optional.

Seal admixtures in which silicon and lead comprise the addition elements, and those comprising silicon and 65 copper as the addition elements, have been found to possess relatively broad maturing temperature ranges of approximately 1325 F. to approximately 1650 F. and about 1325 F. to about 1600 F. respectively.

Particularly excellent results have been obtained with seals produced from admixtures containing silicon, bismuth and lead as the addition elements, such admixtures possessing a low temperature maturing range of from about 1275 F. to about 1500 F. A preferred composition range for this type of seal comprises from about 75 60 parts to parts of a lead-silicate glass, from about 2 parts to 3 parts of silicon, from about 10 pants to 15 parts of bismuth, from about 6 parts to 8 parts of lea-d, and from about 10 parts to 12 parts of aluminum.

In addition to Glass A, various other lead-silicate type glass compositions may be successfully employed in the batch admixtures in accordance with the invention. For example, excellent seals are produced when utilizing in the batch admixture, a glass consisting of 74.37% PbO, 3.77% SiO 8.89% A1 and 9.72% B 0 said glass having an ignition loss of 3.25%. A further specific example of a glass composition that may be successfully employed in producing electrically conducting, substantially gas impervious seals in accordance with the invention, consists of 66.6% of PbO, 23.5% of SiO;.;, 2.9% of A1 0 and 7.0% of B O Although bentonite is not an essential ingredient in the sealing admixture produced in accordance with the present invention, it has been found desirable to include it in such admixtures in order to promote the expansion of the sealing material upon firing. In this respect, seals that expand into a vesicular structure upon firing and occupy, after cooling, a volume greater than before such firing, having been found to be of particular advantage when employed in spark plug assemblies. It has been found that the presence of bentonite in sprak plug seal compositions lowers by several hundred degrees the temperature at which such expansion takes place. The expanded, vesicular seals, generally, are the subject of United States Patent No. 2,898,395.

In addition to the essential ingredients of the glass seal admixtures according to the invention, as previously set forth, various other filler type materials, such as silica and alumina, may be added thereto without deleteriously affecting the essential properties of seals produced therefrom. In this respect further, the use of graphite in the seal admixtures according to the invention has been found to be optional, satisfactory results being obtained either with or without a small amount of graphite in the admixture.

It will be appreciated that the present invention provides an admixture which, when fired in a particular temperature range, undergoes unique reaction resulting in a novel, gas impervious, electrically conducting sealing material, as well as a new and useful spark plug assembly employing such sealing material. While the foregoing description is considered to be of the more advantageous embodiments of the invention, it is obvious that many modifications and variations can be made in the specific compositions and procedures discussed without departing from the spirit and scope of the present invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention as defined by the appended claims.

What we claim is:

1. An electrically conducting substantially gas impervious sealing material produced by firing to a temperature from about 1250" F. to about 1750 F. a composition In general, such glasses should contain from about 3% to about 50% of S102, and from about 20% to about 80% of PDQ. Optimum glasses also contain from about to about 15% of B203.

consisting essentially of: from approximately 55 parts to approximately 85 parts 'by weight of lead silicate glass, from approximately 6 to approximately 20 parts by weight of aluminum, said lead-silicate glass and aluminum being in a weight ratio of at least about 55 to 6, and from approximately 10 to approximately 40 parts by weight of metal particles wetted by lead and not appreciably oxidized by the lead oxide of the glass at said firing tempera ture, the ingredients being proportioned and combined to produce a glassy material having an electrically conductive phase of lead deposited in situ and restrained against migrating from the seal material by the wetted and nonoxidized metal particles.

2. The sealing material of claim 1 wherein said wetted and non-oxidized metal comprises: from 2 parts to 28 parts of at least one high melting metal selected from the group consisting of silicon, nickel, copper, silver, platinum, chromium, and cobalt, and from 7 parts to 29 parts of at least one low melting metal selected from the group consisting of bismuth, lead, and lead-tin solders having a melting point not higher than 350 C.

3. The sealing material of claim 1 wherein said leadsilicate glass comprises from 55 to 60 parts, said aluminum comprises 8 to 20 parts, and said wetted and non-oxidized metal comprises from 15 to 40 parts.

4-. The sealing material of claim 2 wherein said leadsilicate glass comprises from 55 parts to 60 parts, and said aluminum comprises from 8 parts to 20 parts.

5. The sealing material of claim 1 wherein said lead silicate glass comprises from 60 parts to 72 parts, said aluminum comprises from 10 parts to 15 parts, and said wetted non-oxidized metal comprises from 10 parts to 30 parts.

6. The sealing material of claim 2 wherein said leadsilicate glass comprises from parts to 67 parts, said aluminum comprises from 10 parts to 13 parts, said high melting metal comprises from 2 parts to 5 parts of silicon, and said low melting metal comprises from 15 parts to 20 parts of a lead-tin solder having a melting point not higher than 350 C.

7. The sealing material of claim 2 wherein said leadsilicate glass comprises from 57 parts to parts, said aluminum comprises from 10 parts to 14.5 parts, said high melting metal comprises from 2 parts to 27 parts, and said low melting metal comprises from 7 parts to 27 parts.

References Cited by the Examiner UNITED STATES PATENTS 2,106,578 1/ 1938 Schwartzwalder et al.

252509 X 2,267,571 12/1941 McDougal 252512 X 2,415,036 1/1947 Quinn 252512 2,416,480 2/ 1947 Henry et al. 252511 2,890,964 6/ 1959 Commons et a1. 106-48 3,037,140 5/1962 Schurecht 252513 X 3,080,328 3/1963 Billian 252513 JULIUS GREENWALD, Primary Examiner.

ALBERT T. MEYERS, Examiner. 

1. AN ELECTRICALLY CONDUCTING SUBSTANTIALLY GAS IMPERVIOUS SEALING MATERIAL PRODUCED BY FIRING TO A TEMPERATURE FROM ABOUT 1250*F. TO ABOUT 1750*F. A COMPOSITION CONSISTING ESSENTIALLY OF: FROM APPROXIMATELY 55 PARTS TO APPROXIMATELY 85 PARTS BY WEIGHT OF LEAD SILICATE GLASS, FROM APPROXIMATELY 6 TO APPROXIMATELY 20 PARTS BY WEIGHT OF ALUMINUM, SAID LEAD-SILICATE GLASS AND ALUMINUM BEING IN A WEIGHT RATIO OF AT LEAST ABOUT 55 TO 6, AND FROM APPROXIMATELY 10 TO APPROXIMATELY 40 PARTS BY WEIGHT OF METAL PARTICLES WETTED BY LEAD AND NOT APPRECIABLY OXIDIZED BY THE LEAD OXIDE OF THE GLASS AT SAID FIRING TEMPERATURE, THE INGREDIENTS BEING PROPORTIONED AND COMBINED TO PRODUCE A GLASSY MATERIAL HAVING AN ELECTRICALLY CONDUCTIVE PHASE OF LEAD DEPOSITED IN SITU AND RESTRAINED AGAINST MIGRATING FROM THE SEAL MATERIAL BY THE WETTED AND NONOXIDIZED METAL PARTICLES. 